The long term goal of the proposed research is to understand the molecular mechanism regulating plant disease resistance. The knowledge gained from this work could likely be used to genetically engineer disease resistance crops. The use of genetic engineering to protect plants from devastating microbial pathogens will help eliminate the need for toxic chemicals and pesticides, which will have obvious benefits on the health of the environment and its inhabitants. In addition, this work will provide insight into the similarities between the plant and animal defense responses. The proposed research is specifically aimed at understanding the function of a protein (NPR1) that regulates the plant immune response known as systemic acquired resistance (SAR). Sequence analysis suggests that NPR1 may localized to the nucleus and be involved in protein-protein interactions. Furthermore, NPR1 displays similarities to signal transduction components involved in animal defense responses. A fusion of NPR1 with the green fluorescent protein (GFP) is being used to determine the subcellular localization of NPR1 and to analyze the mechanism by which NPR1 regulates the SAR defense response. Localization of this fusion protein in a variety of SAR mutant backgrounds will also be used to help genetically define the SAR signal transduction pathway with respect to NPR1. Additional experiments designed to determine the function of NPR1 are aimed at identifying SAR components that interact with NPR1. This will be accomplished genetically be characterizing supressors of npr1, and molecularly by using interaction cloning and the yeast two hybrid screen.